Air pressure

[rczap]

So peeps I am counting on all of you. My first track day, looking for a good start for my tire pressures.

[maytag]

Originally Posted by rczap

So peeps I am counting on all of you. My first track day, looking for a good start for my tire pressures.

What tire?
What brakes?
Any mods to your car? (Not that it matters much)

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[Topless]

I generally start at 28 cold all around and adjust to 35 hot all around. This is with street tires or NT-01s.

Hot pressure as you come off the track is the important bit. Cold pressures may vary 3-4 psi depending on the heat of the day and whether you drove off a trailer or drove the car to the track.

[Quadcammer]

I aim for 33 hot on nt01. I start at 30 cold and bleed a lot after first session

[maytag]

We really need to know what tire he's using.
Don't ask me why i know, but the Michelin Pilot as3 works best at the track at around 38 or 39 PSI, hot. The sidewall is far too soft at any pressures lower than that.
But the federal 595 rs-rr seems to work best with 35 in the front, 36 in the rear. Again, hot.
But the ability to put heat into the tire, and thus raise that temperature and pressure, is really going to come down to braking.

Tires heat up from flexing. Yes, cornering loads will Flex the sidewall as well, but most of the flexing happens under braking, especially on low horsepower cars like ours.

That's why I asked what brakes he will be using as well. If he is using something like an oem brake pad, then he is not likely to be able to generate a lot of heat into that tire, before losing his brakes.

Let's not lose sight of the fact that pressure is really secondary. What we are really looking for is temperature. Pressure is simply how we manage that temperature.

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[rczap]

Thanks guys, stock 986S on Firestone Firehawk Indy's

[maytag]

Originally Posted by Quadcammer

I aim for 33 hot on nt01. I start at 30 cold and bleed a lot after first session

This seems to confirm what I've been seeing: that the rules I used racing superbikes may also apply here. Namely: I look for a 10-12% rise in pressure, from cold to hot.

With bikes, it's quite common for rookies to start too low cold, then see the pressure spike high because the temperature is too high. They mistakenly bleed air (cuz their hot pressure is too high) making the problem even worse. Tires don't last long this way. Haha. I typically start cold at about 10% under where I want my hot pressure to be, and then bleed off when they're hot.

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[Van914]

I have been told by my suspension guru, that the tire engineers he speaks too, say to run street and DOT Street tires at normal pressures. I have taken his advise and run my RE71's at 34 F / 30 R Cold.
Tires do not were as much. I do bleed back to these pressures after the first run. No more Groove Of Doom!

[rczap]

I just wanted to say thanks for the help on this. I worked towards hot pressures of 35 in the front and 33 in the rears. The tires did well, yes the do get a bit greasy as the track warmed up a bit in the afternoon. I will try to get some video up later this week. My first track day was a complete success and way too much fun!

[Burg Boxster]

Originally Posted by maytag

We really need to know what tire he's using.
Don't ask me why i know, but the Michelin Pilot as3 works best at the track at around 38 or 39 PSI, hot. The sidewall is far too soft at any pressures lower than that.
But the federal 595 rs-rr seems to work best with 35 in the front, 36 in the rear. Again, hot.
But the ability to put heat into the tire, and thus raise that temperature and pressure, is really going to come down to braking.

Tires heat up from flexing. Yes, cornering loads will Flex the sidewall as well, but most of the flexing happens under braking, especially on low horsepower cars like ours.

That's why I asked what brakes he will be using as well. If he is using something like an oem brake pad, then he is not likely to be able to generate a lot of heat into that tire, before losing his brakes.

Let's not lose sight of the fact that pressure is really secondary. What we are really looking for is temperature. Pressure is simply how we manage that temperature.

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Interesting choice running AS tires on track as a regular course.

Anyhow, most novices will heat up tires more via cornering versus braking.

Regardless, the ever so simple rule to follow (except when behind wheel - LOL) is your tires capabilities are 100% the sum of the following accelerating + braking + cornering. The combination doesn't matter the tires cannot exceed 100% sum.

Good luck

[maytag]

Originally Posted by Burg Boxster

Interesting choice running AS tires on track as a regular course.

Yeah.... when I corded a tire in the last session on a Saturday afternoon, the choice I was faced with was: a) miss Sunday altogether, or b) go with the tires I had sitting at home in the garage.
So I spent Sunday sideways in, sideways out, and giggling the whole time! :-)

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[NewArt]

Originally Posted by maytag

Yeah.... when I corded a tire in the last session on a Saturday afternoon, the choice I was faced with was: a) miss Sunday altogether, or b) go with the tires I had sitting at home in the garage.
So I spent Sunday sideways in, sideways out, and giggling the whole time! :-)

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Haha, I like this guy!:dance:

[Geof3]

I look for about 10% as well but also use the good ‘ol chalk line at the tires edge. If I’m using the entire tire, my pressures are good. On “street” tires I’m around 26-27f 30ish Rear. I’m also on 8.5x19 and 10.5x19 rims.